The present invention relates to packaging tubes of the so-called flexible type, i.e., tubes with a tube body manufactured from material which allows the body to be squeezed for emptying the packaging contents. More precisely,, the present invention relates to flexible packaging tubes with an intermediate wall which forms two product-receiving compartments in the tube, the compartments being separated from one another.
Such packaging tubes are used for allowing the containment of different product types as well as for delivering a mixture of the products which is obtained in-situ.
The present invention is intended to provide a method and apparatus for end closure of such intermediate wall tubes, as distinguished from so called twin tubes (see for instance applicant""s own International Application No. WO 94119251).
Tubes with intermediate walls are manufactured, inter alia, by starting from web-like flexible material, e.g., polyethylene, polypropylene or other thermoplastic materials, in a longitudinal direction, by joining, along a pair of welded seams, a material layer serving as an outer tube wall to a material layer serving as an intermediate wall, which intermediate wall material layer is normally thinner than the outer material layer. The width of the outer material web is thereby larger than the width of the material web which is intended to form the intermediate wall, and the relationship between the widths is often chosen so that after longitudinal sealing of the outer layer and forming this into a circular tube, the intermediate wall presents a length over the cross-section of the tube which exceeds the diameter of the tube. The length of the intermediate wall is often chosen so that it corresponds to half the circumference of the tube, which means that with so-called planar sealing of the filling end of the tube, the intermediate wall presents the same length as the flattened tube end during sealing, as well as afterwards.
It has, however, shown itself to be the case that this surplus of length in the intermediate wall, which can be advantageous in the ready-sealed tube end, results in difficulties, even at the filling stage.
In order to overcome this, the applicant previously produced a method and device (WO 98/54054, priority date May 27, 1997), which allows the introduction of the filling nozzle on respective sides of the intermediate wall. Two relatively well-defined spaces in the closure end of the packaging tube are thereby created by the intermediate wall being stretched and spot welded to the inside of the tube at two substantially diametrically opposed positions.
This spot welding is done in a filling machine and, for continued efficient handling in the machine after filling with product/products, the filling end of the tube with corresponding end of the intermediate wall has to be capable of being sealed in a rational manner to form an end closure.
Tubes with intermediate walls are also manufactured by injection molding, in one-piece, a tube body, breast and intermediate wall.
Due to this manufacturing method, the intermediate wall in this case is of a thicker material as compared to the first-mentioned type of intermediate wall tube.
The greater material thickness results in problems with sealing the tube end.
In order to achieve such sealing, the intermediate wall has been allowed to finish at a distance from the tube end. With the aid of contacting heated jaws, heat energy from the outside of the tube is supplied to the inside of the tube in an encircling end area of the tube at a level above the intermediate wall.
Thus, in the tube filling machine, directly after the heat-activation station following the embossing station, embossing jaws operating perpendicularly to the intermediate wall during the entire sealing process have been used to press the ends of the tube together in the encircling end area in order to thereby create a seal.
However, such a seal does not always ensure the production of a joint which is free of passages between the two product containing compartments, which the intermediate wall is intended to achieve.
One object of the present invention is to solve the problem of end closure of packaging tubes of the types mentioned above, and to provide a solution which, while maintaining productivity in a tube filling machine, provides a complete handling of intermediate wall tubes, in principle in a manner which is equal to the highly effective handling of conventional tubes.
The solution to these problems should furthermore be such that a minimum of disturbance is required in existing tube filling lines.
In accordance with the present invention, these and other objects have now been realized by the discovery of a method for the end closure of a packaging tube including a tube body having a filling end and an intermediate wall forming a pair of separated product-receiving compartments, the intermediate wall extending across the tube body substantially along the entire length of the tube body along a first pair of circumferentially spaced joining locations, and a second pair of circumferentially spaced joining locations at the filling end of the tube body, whereby predetermined portions of the intermediate wall are formed between each of the second pair of circumferentially spaced joining locations and each of the first pair of circumferentially spaced joining locations, the method comprising heat activating the intermediate wall and the inside of the tube body by inserting a hot air nozzle including a pair of sub-members forming a gap therebetween into the area of the filling end of the tube body without direct contact with the packaging tube while applying a forming tool externally to the filling end of the tube body whereby the cross-sectional dimension of the filling end is compressed in both the horizontal and vertical directions, the intermediate wall is maintained in a stretched condition in the filling end of the tube body and both of the predetermined portions of the intermediate wall are brought closer to the inside of the tube body than before application of the forming tool, subsequently removing the hot air nozzle, and clamping the packaging tube so as to seal the filling end of the tube body.
In accordance with one embodiment of the method of the present invention, the tube body comprises a substantially elliptical shape and the intermediate wall is stretched across a minor axis of the filling end of the tube body, and wherein the applying of the forming tool externally to the filling of the tube body provides a cross-sectional dimension of the tube end having a substantially right-angled, four-sided shape. In a preferred embodiment, the pair of sub-members of the hot air nozzle comprise a pair of substantially identical sub-members defining substantially a right-angled cross-sectional dimension forming the gap adapted to receive the intermediate wall.
In accordance with another embodiment of the method of the present invention, the method includes inserting the hot air nozzle into the area of the filling end of the tube body so that the concentration of heat energy obtained on the intermediate wall is provided at portions of the intermediate wall between the first and second pairs of circumferentially spaced joining locations.
In accordance with the present invention, apparatus has also been discovered for the end closure of a packaging tube including a tube body having a filling end and an intermediate wall forming a pair of separated product-receiving compartments, the intermediate wall extending across the tube body substantially along the entire length of the tube body along a first pair of circumferentially spaced joining locations and a second pair of circumferentially spaced joining locations at the filling end of the tube body, whereby predetermined portions of the intermediate wall are formed between each of the second pair of circumferentially spaced joining locations and each of the first pair of circumferentially spaced joining locations, the apparatus comprising a hot air nozzle including a pair of sub-members forming a gap therebetween for accommodating the intermediate wall, the pair of sub-members including hot air delivery openings in the gap and outside of the gap, the hot air nozzle being dimensioned for insertion into the filling end of the tube body without directly contacting the packaging tube whereby the tube body including the intermediate wall at the filling end can be heat activated, clamping means for clamping and sealing the heat activated regions of the tube body, and a forming tool for external application to the filling end of the tube body during the heat activation to compress the filling end in both the horizontal and vertical directions, to maintain the intermediate wall in a stretched condition in the filling end of the tube body, and to bring both of the predetermined portions of the intermediate wall closer to the inside of the tube body than before application of the forming tool. In a preferred embodiment, the forming tool includes cooling means, the forming tool including an inner surface providing a substantially four-sided forming opening for application to the filling end of the tube body.
The solution to the problem underlying the present invention, when dealing with packaging tubes of the above-mentioned type, is found by the realization that it is possible, in the present connection of material wall thicknesses of a highly varying degree and material of different types, as well as with addition of material layers in different areas of the produced sealing area, with the method and apparatus described above to heat-activate the complicated material composite or geometry, respectively, so that acceptable heat sealing is obtained in all areas of the produced end closure, also including any areas with double-layered intermediate walls and areas with up to and including triple intermediate walls.
The solution to the problems underlying the present invention, when dealing with the packaging tubes of the second type mentioned, is found by the realization that it is possible, in the present connection of material wall thicknesses achievable by injection molding and with the intermediate wall finishing at the level of the tube end or at a distance from it, with the method and apparatus, respectively, to heat-activate and thereafter press together the complicated material geometry so that acceptable heat sealing is obtained in all areas of the end closure which is created, including also any areas where the intermediate wall is present.